DE29609624U1 - Measuring device for measuring the mass flow of a flowing medium - Google Patents

Description

PATENT ATTORNEYS

DÜSSELDORF-ESSEN DIPL.-PHYS.DR. PETER PALGEN

dipl.-phys.DRH. SCHUMACHER

EUROPEAN PATENT ATTORNEYS

OUR SIGN: Dr.K/me DÜSSELDORF,

28.05.1996

Bopp & Reuther Messtechnik GmbH in 68305 Mannheim

Measuring device for measuring the mass flow of a flowing

Media

The invention relates to a measuring device for measuring the mass flow of a flowing medium of the type corresponding to the preamble of claim 1.

If an essentially U-shaped pipe loop through which a medium flows is rotatably mounted at the two open ends of the pipe and is rotated about the axis of rotation, a Coriolis force couple acts on the two sections of the pipe loop. This force couple is caused by the different flow directions of the medium in the inlet and outlet sections. The force couple twists the U-shaped pipe about an axis that lies in the plane of the pipe and runs parallel to the inlet and outlet sections.

If the rotational movement of the U-shaped tube is replaced by a back and forth oscillation, the so-called fundamental oscillation, the force pairs also oscillate back and forth as the angular velocity is reversed. This creates a torsional oscillation around the axis described above that is superimposed on the fundamental oscillation. Since the Coriolis forces are proportional to the mass flow through the tube, the amplitude of the torsional oscillation depends on the mass flow.

Measuring devices that exploit this phenomenon to measure mass flow have been known for some time - for example from WO 90/15310. The disadvantage of these measuring devices is that the torsional stiffness of the U-shaped tube around the oscillation axis is naturally considerably higher than the bending stiffness around this axis, so that the measuring signal is relatively small, meaning that small flow rates or mass flow of a medium with low density cannot be reliably recorded.

To improve these disadvantages, DE-OS 33 29 544 A1 therefore provides for the U-shaped pipe loop to be excited to a primary rotational (basic) oscillation around an axis of rotation that runs parallel to the lateral legs and intersects the free apex of the pipe loop in the middle using a vibration generator. This primary rotational (basic) oscillation causes Coriolis forces in the apex of the pipe loop in conjunction with a mass throughput, which result in a translational deflection of this pipe loop part that is shifted by 90° against the basic oscillation and is proportional to the flow and is superimposed on the primary basic oscillation. This translational deflection manifests itself as an oscillation of the apex of the pipe loop around an oscillation axis that is perpendicular to the axis of rotation of the torsional (basic) oscillation in such a way that the pipe loop oscillates back and forth around the oscillation axis that runs through the two ends of the pipe loop. In this mass flow meter, the Coriolis force pair therefore causes a bending oscillation around an oscillation axis, around which the bending stiffness of the pipe loop is considerably lower than that around the oscillation axis of the torsional oscillation caused by the Coriolis force pair in the first-mentioned mass flow meters.

In the mass flow meters known from DE-OS 33 29 544 that operate according to this principle, the ends of one or two opposing U-shaped pipe loops are anchored in a rigid loop holder. The loop holder is mounted on a

Shaft is rotatably mounted, the central axis of which runs parallel to the legs of the pipe loop in the middle between them and lies in the plane spanned by the pipe loop. With the help of an electromagnetic vibration generator that works together with the loop holder, the pipe loop is excited into a primary rotational (basic) vibration around this axis. With the help of electromagnetic vibration sensors that work together with the apex of the pipe loop, the amplitude of the bending vibration caused by the Coriolis force pair or the phase shift of the rotational (basic) vibration caused by this is registered. Although it is possible with this device to register smaller mass flows due to its inherently higher measurement sensitivity, in practice the rotatable mounting of the loop holder on the shaft, which is also dynamically stressed by the Coriolis vibration, leads to considerable difficulties with regard to the measurement value stability of the mass flow meter. Furthermore, this mass flow meter is very complex to manufacture and is also sensitive to external interference.

The invention is therefore based on the object of further developing a generic mass flow meter in such a way that it is improved in terms of its functionality and relatively easy to manufacture.

This object is solved by the invention set out in claim 1.

In the measuring device according to the invention, the legs of each pipe loop are curved in such a way that their end areas have directional components that are approximately parallel to the apex of the respective pipe loop and lie on a common axis in the plane of the pipe loop. On the one hand, this measure ensures that in the event of a mass flow, the pipe loop carries out a particularly clean and stable Coriolis oscillation around the oscillation axis defined by the common axis of the directional components. On the other hand,

On the one hand, the two free vertices of the two pipe loops can be excited into mutually antiphase, primary rotational (fundamental) oscillations, whose axes of rotation run in the plane of the respective pipe loop transversely to the corresponding oscillation axis of the Coriolis oscillation, without the need for a rotatable mounting of the two pipe loops, since the directional components of the end regions of the legs parallel to the vertex of the pipe loop are subjected to bending stress, which ensures an amplitude of the rotational (fundamental) oscillation sufficient to generate the measuring effect while at the same time ensuring insensitivity to interference.

The insensitivity to external disturbances can be further increased by the fact that the clamping pieces intended for fixing the end regions of the opposite legs of the two pipe loops (claim 2) are designed as mass bodies according to claim 3.

The sensitivity to external disturbances can be further reduced by connecting the clamping pieces according to claim 4 via a solid bridge.

A particularly advantageous design of the pipe loops is the subject of claims 5 to 9. A correspondingly designed pipe loop has the shape of a "trumpet pipe" mirrored on the axis of rotation of the rotational (fundamental) oscillation in its side view, with each leg of a pipe loop having a first and a second straight pipe section, which each runs parallel to the straight vertex of the pipe loop. Since these straight sections of the legs are subjected to bending stress by the primary rotational (fundamental) oscillation, the amplitude of the rotational (fundamental) oscillation is particularly large in this preferred design of the pipe loops, which further increases the measuring sensitivity of the measuring device. Furthermore, the first and second 180° pipe bends increase the bending length of the legs that is effective for the Coriolis oscillation, which also benefits the increase in the measuring sensitivity of the measuring device.

If the medium flows through both pipe loops of the measuring device in the same direction, the measuring effects caused by the respective Coriolis force pair in the pipe loops add up. It is therefore advantageous according to claim 10 to provide the opposite ends of the legs of the pipe loops with connecting pipes that lead into a common flow divider, so that the flow of the medium is divided on the inlet side and reunited on the outlet side.

The flow dividers according to claim 11 can be accommodated in a particularly space-saving manner in connection flanges for connecting the measuring device to a pipeline.

The measuring device can be manufactured particularly efficiently and is equally effectively decoupled from external interference if the connecting pipes also serve to hold the pipe loop arrangement in a housing extending between the connecting flanges and surrounding the pipe loop arrangement.

Tests have shown that the greatest immunity to interference of the measuring device is achieved when the connecting pipes according to claim 13 run symmetrically to the center plane of the pipe loop arrangement formed by the two pipe loops, obliquely from the respective flow divider to the ends of the legs of the pipe loops.

In a first preferred embodiment of the measuring device, the vibration generator and the device for measuring the phase shift caused by the Coriolis torsional vibration are designed according to claims 14, 15 and 16. This embodiment can be produced particularly inexpensively and already meets high requirements for the stability of the measured value.

A further, particularly preferred embodiment of the measuring device is the subject of claims 17, 18 and 19. In this embodiment, the excitation and pickup coils arranged in the manner described in claims 17 and 18 are mounted on a common base,

which is detachably connected to the clamping pieces and/or to the bridge. This version of the measuring device is more complex to manufacture than the one described above, but it has an even higher measurement accuracy. Furthermore, in this version the coils can be replaced completely together with the base without great effort, for example in the event of a defect.

The drawing shows two exemplary embodiments of the measuring device according to the invention. They show:

Fig. 1 is a view from above of the part of the measuring device that is identical for both embodiments, in which the vibration generator and the device for measuring the phase shift have been omitted;

Fig. 2 shows a first embodiment in a side view of the pipe loop arrangement (view A in Fig. 3);

Fig. 3 is a section through the pipe loop arrangement along line III-III in Fig. 2;

Fig. 4 a second embodiment in a side view of the pipe loop arrangement (view B in Fig. 5;

Fig. 5 is a section through the pipe loop arrangement along line V-V in Fig. 4 and

Fig. 6 the lateral course and the phase positions of the oscillations of the free peak of one of the two pipe loops in the case of a mass flow.

The measuring device, designated as a whole with 100 in Fig. 1, comprises a cuboid-shaped housing 1, on the narrow end faces of which a connecting flange 2, 2' is provided for connecting the measuring device 100 to a pipeline system not shown in the drawing.

Each connector 2,2' has a flow divider 4,4' in its central through-hole 3,3', which divides the flowing medium on the inlet side into two pipe loops.

··· · &phgr; » &iacgr;&idigr;

connection pipes 5,6 serving for the connection 10, on the output side the divided flows are brought together via the connection pipes 5',6'. The connection pipes 5,6 and 5 ',6', which also serve to hold the pipe loop arrangement 10 in the housing 1, form the same angle α with the center plane E of the pipe loop arrangement 10, which will be described in more detail below, resulting in a completely symmetrical structure of the measuring device.

The pipe loop arrangement shown in a side view in Figs. 2 and 4 comprises two pipe loops 20, 20' arranged opposite one another in parallel planes E', E'', which will be described using the example of the pipe loop 20 facing the viewer in Figs. 2 and 4.

The pipe loop 20, which is produced in one piece by bending a pipe with a circular cross-section, comprises a straight apex 21, to which first 180° pipe bends 22, 22' curved in the same direction are connected on both sides. The pipe bends 22, 22' are followed by straight pipe sections 23, 23', the center axes of which lie on a common axis S ₁ which runs parallel to the straight apex 21.

The straight pipe sections 23, 23', each of which is approximately one third of the length of the apex 21, merge into second 180° bends 24, 24' curved towards the inside of the pipe loop, which in turn lie in the plane E' or E'' of the pipe loop 20 or 20'. The radius of curvature of the second 180° pipe bend 24, 24' is approximately 60% of the radius of curvature of the first pipe bend 22, 22'.

The pipe bends 24,24' are followed by second, straight pipe sections 25,25', the open ends 26,26' and 27,27' of which are connected to the connecting pipes 5,5' and 6,6' respectively. The center axes of the straight pipe sections 25,25' lie on a common axis S ₂ .

The pipe bends 22,22', the pipe sections 23,23', the pipe bends 24,24' and the pipe sections 25,25' form the lateral legs 28,28' of a pipe loop 20 or 20'.

In the embodiment of the measuring device shown in Fig. 2, the torsional (fundamental) oscillation is excited by a vibration generator 30 which comprises two excitation coils 31, 31' arranged on the outer surface of the free apex 21 of one pipe loop 20 facing away from the pipe loop interior, spaced apart by the same amount from the symmetry axis D of the pipe loop 20 running perpendicularly to the axes S ₁ and S ₂ , with the coil axes perpendicularly intersecting the center plane E of the pipe loop arrangement, which are opposite two excitation magnets 32 provided on the apex of the other pipe loop with the poles pointing in the direction of the coil axes - as can be seen from Fig. 3.

To measure the phase shift of the rotational (fundamental) vibration caused by the Coriolis force pair in the event of a mass flow, two pickup coils 33 are arranged on the surface of the free leg (21) of one pipe loop facing away from the pipe loop interior, spaced apart from the axis of symmetry D by the same amount, adjacent to the excitation coils towards the axis of rotation, with the coil axes perpendicularly intersecting the center plane E of the pipe loop arrangement 10, which are opposite two pickup magnets 34, 34' provided on the vertex of the other pipe loop with the poles pointing in the direction of the coil axis.

The pipe loops 20, 20', which are located opposite one another in parallel planes and together form the pipe loop arrangement 10, are fixed to one another by means of two-part clamping pieces 11, 12, which encompass the end areas of two opposite pipe sections 25 and 25' of the two pipe loops 20, 20' in their end areas. The parts 11', H'' and 12', 12'' have an approximately semicircular recess in cross-section to accommodate the pipe sections, so that the pipe legs are almost completely clamped. The clamping of the two parts 11', H'' and 12', 12'' of the clamping pieces 11, 12 can be carried out using one or more clamping screws not shown in the drawing or in any other way that ensures a secure hold.

_t J ,·♦ ·* ··*· »· tttt

—9—

of the clamped pipe sections in the clamping pieces 11,12.

The clamping pieces 11, 12, which are designed as mass bodies to better decouple the pipe loop arrangement 10 from external interference, are connected to one another via a solid bridge 13, which further reduces the susceptibility of the measuring device to interference. The clamping pieces 11, 12, together with the bridge 13, form a pipe loop holder 14.

The preferred embodiment shown in Figs. 4 and 5 differs from that shown in Figs. 2 and 3 only in the design of the vibration generator and the device for measuring the phase shift caused by a Coriolis force pair, so that at this point reference is made to the explanations relating to Figs. 2 and 3 with regard to the pipe loop arrangement 10. Components with the same function are therefore provided with the same reference numerals.

As can be seen in Fig. 5, in this further embodiment a base 35 is provided, the center plane of which coincides with the center plane E of the pipe loop arrangement 10.

On the surface of the free vertex facing away from the inside of the pipe loop, excitation magnets 38, 38' are arranged opposite one another and spaced apart by the same amount from the respective axis of symmetry D, whereby the axis defined by the poles of the magnets facing one another intersects the center plane E of the pipe loop arrangement perpendicularly. The magnets are arranged in such a way that the south pole of one magnet is opposite the north pole of the other. Excitation coils 36, 36' are provided between the excitation magnets 38 and 38' facing one another and are attached to the base.

In a corresponding manner, opposite to the axis of rotation, spaced apart by the same amount,
pickup magnets 39,39' adjacent to the excitation magnets towards the axis of rotation on the lateral surfaces of the free legs facing away from the pipe loop interior

the pipe loops 20, 20', which in turn interact with pickup coils 37 arranged between opposite pickup magnets 39 and 39'.

This embodiment, which is somewhat more complex to manufacture than the one shown in Fig. 2 and 3, has the advantage that - for example in the event of a defect - all coils 36, 36', 37, 37' can be easily replaced together with the base. Furthermore, no electrical cable is required on the pipe loops 20, 20', which could potentially influence the vibration behavior of the pipe loops. As a result, the measurement value stability of this second embodiment is again increased compared to the one shown in Fig. 2 and 3.

In the following, the functionality of the measuring device according to the invention will be explained.

For example, the measuring medium - usually a liquid or a gas - is fed to the two pipe loops 20, 20' of the pipe loop arrangement 10 via the flow divider 4 and the connecting pipes 5, 6. The flow direction is symbolized by the arrows P. The flowable medium flows in sequence through the legs 28, the free vertices 21 and the legs 28' of the two pipe loops 20, 20'.

With the help of the excitation coils 31,31' and 36,36' acting on the excitation magnets 32 and 38,38', respectively, the free vertices 21 of the two pipe loops 20,20' are set into opposite primary rotational (basic) oscillations around a rotation axis B^, which coincides with the axis of symmetry D of the respective pipe loop arrangement 20,20'.

As long as the pipe loop arrangement 20, 20' is not flowed through by the flowable medium, the ends of the free vertices 21 of the pipe loops 20, 20' carry out essentially sinusoidal oscillations, which are 180° out of phase with each other. These oscillations are shown for the ends of one of the two free vertices 21 in Fig. 6 A and B with the solid lines. Due to the fundamental rotational oscillations of the

At the two free vertices 21 of the pipe loops 20, 20', the straight pipe sections 23, 25 and 23, 25' of the legs 28 and 28' are essentially subjected to bending stress, whereby a sufficiently large amplitude of the rotational (basic) vibrations of the vertices 21 is achieved due to the relatively low bending stiffness compared to the torsional stiffness of a pipe, without the need for a rotatable mounting of the pipe loops 20, 20' about the rotation axes Di.

As soon as the measuring medium flows through the pipe loops 20, 20' in the manner described, Coriolis forces arise under the influence of the rotational oscillation taking place around the rotational axis Di in the corresponding vertex 21, the size of which is proportional to the respective flow and tends to deflect the respective vertex 21 around an oscillation axis running perpendicular to the rotational axis Di. The deflection caused by the Coriolis forces occurs due to the shape of the legs 28, 28' of the pipe loops 20, 20', which is curved twice by 180°, the direction of which changes periodically with the rotational oscillation of the vertex 21 around the rotational axis Di, around the oscillation axes defined by the straight pipe sections 23, 25 or 23', 25' of the two legs 28, 28'.

Claims (19)

PATENT ATTORNEYS DÜSSELDORF · ESSEN DIPL.-PHYS. DR. PETER PALGEN DIPL.-PHYS. DR. H. SCHUMACHER EUROPEAN PATENT ATTORNEYS our reference: Dr.K./me DÜSSELDORF, 28.05.1996 Bopp & Reuther Messtechnik GmbH in 68305 Mannheim Protection claims 1. Measuring device for measuring the mass flow of a flowing medium, in which the Coriolis force acting on the flowing medium is used to generate a measured value for the mass flow, with two pipe loops 20, 20' through which the medium flows and which are arranged opposite one another in approximately parallel planes (E', E''), each of which has a free apex (21) and two legs (28, 28') bent in the same direction from these, with a pipe loop holder (14) which receives the legs (28,28') in their end areas, with a vibration generator (30) which sets the free vertices (21) into an antiphase, each oscillating about a rotational axis (Di) lying in the plane (ε',ε'') of the respective pipe loop (20,21) rotational (basic) vibration and with a device for measuring the phase shift of the torsional (fundamental) oscillation, which in the case of a mass flow is caused by the Coriolis torsional oscillation of each pipe loop caused by the Coriolis force around an oscillation axis running transversely to the axis of rotation (Di), · I characterized, that the legs (28,28') of each pipe loop (28,28') are curved in such a way that their end regions have directional components that are approximately parallel to the vertices (21) of the respective pipe loop, approximately in the plane (E'/E'') of the pipe loop and approximately on a common axis, and that the end areas of the opposite legs of the two pipe loops are fixed against each other. 2. Measuring device according to claim 1, characterized in that the end regions of the opposite legs of the two pipe loops are each fixed against each other by a clamping piece (11, 12). 3. Measuring device according to claim 2, characterized in that the clamping pieces (11, 12) are designed as mass bodies. 4. Measuring device according to claim 2 or 3, characterized in that the clamping pieces (11, 12) are connected to one another via a solid bridge (13). 5. Measuring device according to one of claims 1 to 4, characterized in that the free vertices (21) of the pipe loops (20, 20') are straight. 6. Measuring device according to one of claims 1 to 5, characterized in that the legs (28, 28') comprise first 180° pipe bends (22, 22'). 7. Measuring device according to claim 6, characterized in that the first 180° pipe bends (22, 22') of a pipe loop (20, 20') open into first straight pipe sections (23, 23') whose central longitudinal axes are on a common, in the The axis (Si) running along the plane (E',E'') of the pipe loop. 8. Measuring device according to claim 7, characterized in that the first straight pipe sections (23, 23') of the legs (28, 28') are adjoined by two of the 180" pipe bends (24, 24') which are directed towards the inside of the pipe loop and whose radii of curvature are smaller than those of the first pipe bends (22, 22'). 9. Measuring device according to claim 8, characterized in that the second pipe bends (24, 24') open into second straight pipe sections (25, 25') whose central longitudinal axes lie on a common axis (S2) running in the plane (ε', ε'') of the pipe loop. 10. Measuring device according to one of claims 1 to 9, characterized in that the opposite ends of the legs of the pipe loops are connected to connecting pipes (5,6;5',6') which open into a common flow divider (4,4'). 11. Measuring device according to claim 10, characterized in that the flow dividers (4,4') are integrated in connecting flanges (2,2') for connecting the measuring device to a pipeline. 12. Measuring device according to claim 10 or 11, characterized in that the connecting pipes (5,6;5', ^6f ) equally serve to hold the pipe loop arrangement (10) in a housing (1) extending between the connecting flanges (2,2') and surrounding the pipe loop arrangements (10). 13. Measuring device according to claim 12, characterized in that the connecting pipes (5,6;5',6') are inclined symmetrically to the center plane (E) of the pipe loop arrangement (10) formed by the two pipe loops (20,20'). from the respective flow divider (4,4') to the ends of the legs (28,28') of the pipe loops. 14. Measuring device according to one of claims 1 to 13, characterized in that the vibration generator (30) comprises two excitation coils (31, 31') arranged on the outer surface of the free apex of one pipe loop (20) facing away from the pipe loop interior, spaced apart from the axis of rotation by the same amount, with the coil axes perpendicularly intersecting the center plane (E) of the pipe loop arrangement (10), which are opposed by two excitation magnets (32) provided on the apex of the other pipe loop (20') with the poles pointing in the direction of the coil axes. 15. Measuring device according to claim 14, characterized in that the device for measuring the phase shift of the torsional (fundamental) oscillation caused by the Coriolis torsional oscillation comprises two pickup coils (33) arranged on the outer surface of the free apex of one pipe loop (20') facing away from the pipe loop interior, spaced apart from the axis of rotation (σχ) by the same amount, adjacent to the excitation coils (31, 31') towards the axis of rotation, with the coil axes perpendicularly intersecting the center plane (E) of the pipe loop arrangement (10), which are opposed by two pickup magnets (34) provided on the apex of the other pipe loop (20) and pointing with the poles in the direction of the coil axes. 16. Measuring device according to claims 14 and 15, characterized in that one pipe loop (20) carries the excitation coils and the pickup magnets, the other pipe loop (20') carries the excitation magnets and the pickup coils. 17. Measuring device according to one of claims 1 to 13, characterized in that the vibration generator (30) has two on the casing facing away from the pipe loop interior surface of the free apex of the one pipe loop (20), spaced apart from the axis of rotation (Di) by the same amount, with the axes connecting the poles perpendicularly intersecting the center plane (E) of the pipe loop arrangement (10), which are opposed by two excitation magnets (38, 38') provided on the apex of the other pipe loop (20, 20'), the poles of which are aligned in accordance with those of the excitation magnets of the one pipe loop, and that excitation coils (36, 36') are provided between the opposing excitation magnets of the two pipe loops, the coil axes of which point in the direction of the axes specified by the poles of the excitation magnets. 18. Measuring devices according to claim 17, characterized in that the device for measuring the phase shift of the rotational (basic) vibration caused by the Coriolis rotational vibration comprises two pickup magnets (39, 39') arranged on the outer surface of the free vertex of one pipe loop (20) facing away from the pipe loop interior, spaced apart from the axis of rotation (Di) by the same amount, adjacent to the excitation magnet towards the axis of rotation (Di), with the axes connecting the poles perpendicularly intersecting the center plane (E) of the pipe loop arrangement (10), opposite which are two pickup magnets (39, 39') provided on the vertex of the other pipe loop (20'), whose poles are aligned in accordance with those of the pickup magnets of one pipe loop, and that pickup coils (37) are provided between the pickup magnets of the two pipe loops lying opposite one another, the Coil axes point in the direction of the axes defined by the poles of the pickup magnets. 19. Measuring device according to claims 17 and 18, characterized in that the excitation and pickup coils are mounted on a common base (35) which can be detached bar is connected to the clamping pieces (11,12) and/or to the bridge (13).